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Author Topic: Why Not Use?  (Read 1834 times)

Offline Bill Sawyer

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Why Not Use?
« on: January 02, 2007, 08:44:05 AM »
In most references to motors I see a trend to use the AXI 2826/10. The advertisements lists it as a 40-46 size engine replacement. In the same ad there is also a AXI 2820/10 listed with a corresponding size of a 40 engine. Is this motor being overlooked in preference to a stronger motor or is everyone looking to have the most power?
Has anyone done any experimenting with the 2820/10?
While I have your attention I have another question or two. What is needed to connect a Randy Smith spinner to one of these motors and who sells the items needed?
« Last Edit: January 02, 2007, 03:30:00 PM by Bill Sawyer »
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Online Mike Palko

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Re: Why Not Use?
« Reply #1 on: January 02, 2007, 03:46:13 PM »
Bill,
   I used an AXI 2820/10 on my Twister back in 2003. It was a great motor, but is only equivalent to a .32-.35 at best. Most of the ARF's being flown require a solid .40 to pull them. Not to mention many are heavy for their size because they were not intended to be electric power.
   
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Kim Doherty

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Re: Why Not Use?
« Reply #2 on: January 03, 2007, 08:05:48 PM »
Bill,

Just to add to what Mike has stated, electric motors do not in and of themselves posses any innate amount of power. In a way, it (electricity) is like having an unlimited boosting effect from nitro. Electric motors are simply energy conversion devices. If you have more volts (power) you can turn a bigger prop with any electric motor. If you have more amps (capacity) you can turn that same prop for a longer time. The issue with the motors is their ability to turn the incoming energy into a rotational force without burning up the windings or causing the magnets to let go from the heat. So with each step up in size of the motor-can you can accommodate more windings and larger magnets thus giving the motor the ability to convert more of the incoming energy into rotation with lower resistive losses.

For the most part the determining factor as to how much power a particular motor is capable of producing (aside from melting) is the battery. More cells in series = more volts = turn bigger prop. More cells in parallel = more mah capacity = turn prop for a longer time.

From the motor's perspective, more turns (copper windings) = turn slower with more torque. Fewer turns = turn faster with less torque. You will see motors identified as "28/26 - 12 and 28/26 - 10". The "10" can turn a given prop faster with less torque vs. the  "12" which has more turns and will turn the same prop slower with more torque. 

Larger motor-cans also produce more torque due to the natural gearing effect of their larger diameter.

Kim.
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Offline Bill Sawyer

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Re: Why Not Use?
« Reply #3 on: January 03, 2007, 08:27:43 PM »
Kim,
   I worked in electronics for 35 years so I understand all of that. I just wanted to know if anyone had experience with the 2820/10. I was considerint tyring one but wanted to get some comments on the motor before I wasted my money.

Bill
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Offline phil c

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Re: Why Not Use?
« Reply #4 on: January 04, 2007, 11:04:20 AM »
Quote from: Bill Sawyer on January 03, 2007, 08:27:43 PM
Kim,
   I worked in electronics for 35 years so I understand all of that. I just wanted to know if anyone had experience with the 2820/10. I was considerint tyring one but wanted to get some comments on the motor before I wasted my money.

Bill

I don't have personal experience, but the the GSCB symposium a couple years ago I talked to Dean Pappas about it.  Running the smaller motor at a higher power level was one thing he was thinking about.  Save a couple ounces on motor weight and run higher voltage.  As Mike says, the problem would be keeping the motor cool, but  the couple articles Dean had in FM last year showed how to do that with ducting.  You can't just hang the motor out in the breeze.  In needs a cowel designed to force cooling air through it.
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phil Cartier

Online Mike Palko

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Re: Why Not Use?
« Reply #5 on: January 04, 2007, 03:56:19 PM »
Quote from: phil c on January 04, 2007, 11:04:20 AM
I don't have personal experience, but the the GSCB symposium a couple years ago I talked to Dean Pappas about it.  Running the smaller motor at a higher power level was one thing he was thinking about.  Save a couple ounces on motor weight and run higher voltage.  As Mike says, the problem would be keeping the motor cool, but  the couple articles Dean had in FM last year showed how to do that with ducting.  You can't just hang the motor out in the breeze.  In needs a cowel designed to force cooling air through it.

   I have looked at many different power system configurations from low voltage/high amperage to high voltage/low amperage. There is no clear winner when it comes to weight.   

   If you draw more current through a small light weight motor you need a heavier battery (due to added capacity) to get the flight time. It will also turn more energy into wasted heat.

   If you run higher voltage through a small light weight motor you again need a heavier battery (due to the added voltage) to get the power back. However, it will more than likely give you more power to the prop for the same weight as low voltage/high amperage setup (less power turned into heat).

   The best combination is the most efficient combination. Using the most efficient motor for your application is going to give you the best results. Some brushless outrunners and cheap Chinese motors have surprisingly bad efficiency (60-75%), nearing the efficiency of high-end brushed motors. I believe most of the AXI motors run in the 80-88% efficiency range. There are motors out there capable of 92-94%. Couple that efficiency with a high voltage/low amperage setup and you will turn less of the available power into wasted heat.

   No matter how efficient the motor is there is a point of diminishing returns. You won't be able to get rid of the heat fast enough and will have to move up to a larger motor.

   The motors and batteries available today are already capable of competing with the best IC engines. As mentioned before you need to get away from the heavy ARF's and scratch build. The fact that you don't need an engine crutch, plywood doublers, and a tank floor/mount makes the power system weight almost equal to an IC setup. Properly applied, the power system technology is here.   
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Offline Dean Pappas

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Re: Why Not Use?
« Reply #6 on: January 10, 2007, 01:42:49 PM »
Hi Gang,
Hi Bill,
The AXI 2820 series is best left for 300W systems rather than the 400 to 500 we typically think of for a 40 replacement.
It'd be dandy for a plane that comes out at 36 ounces complete with battery.
later,
Dean
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